This invention relates to an engine control strategy for a direct injected engine and more particularly to an improved start-up strategy for an engine having a feedback fuel injection control.
In the interest of improving engine performance and particularly fuel efficiency and exhaust emission control, many types of engines now employ fuel injection and/or feedback control of the fuel supply to the engine. Fuel injection has the advantages of permitting the amount of fuel delivered for each cycle of the engine to be adjusted. In addition, by utilizing fuel injection and a feedback control system, it is possible to maintain the desired fuel air ratio under a wide variety of engine running condition.
These features are particularly useful with two cycle engines, although not specifically limited thereto. The utilization of these features with two cycle engines is important, however, because of the emission characteristics of the two cycle engine is somewhat poorer than those of the four cycle engine. This is the result of the fact that the engine fires every revolution and there is a fairly substantial overlap during the scavenging and exhaust cycles.
Generally, these systems operate with a combustion condition sensor such as an oxygen (O.sub.2) sensor that outputs a signal indicating whether the mixture is lean or rich. If the mixture deviates from the desired mixture, then incremental adjustments may be made to bring the mixture back into the desired relationship.
It is also acknowledged that the oxygen sensors or combustion conditioned sensors normally utilized must be at a certain temperature in order to provide a proper output. Therefore, start-up and warm-up conditions are conditions that are difficult to operate under feedback control. Various devices and methodologies have been employed for utilizing other control strategies during starting and warm-up. However, these strategies have some disadvantages and may require operation under a non-feedback control condition for longer than necessary.
It is, therefore, a principal object of this invention to provide an improved engine feedback control system and particularly a start-up and warm-up operation for such system.
It is a further object of this invention to provide an engine feedback control system that has an arrangement wherein feedback control of at least one cylinder is provided during starting and warm-up with the other cylinders have their injection amount based upon the correction made to the fed back cylinder with adjustments being made to compensate for the fact that the sensor output may not be totally reliable under these conditions.